Preheat the oven to 375ºF.

Place the chicken breasts on a cutting board and cut the chicken in half lengthwise with a sharp knife leaving the chicken breast connected, but creating a flap.

Sprinkle the spice rub over the chicken breast on both sides, including in the flap.

Add the cheddar cheese, Greek yogurt, cream cheese, and minced garlic into a large bowl and mix until combined.

Next, add the diced broccoli to the Greek yogurt mixture and mix everything together until the broccoli is coated in the Greek yogurt sauce. 

Divide the broccoli mixture into fourths. 

Stuff a chicken breast with 1/4 of the broccoli mixture by placing it in between the flap. Secure the broccoli cheese filling by closing the flap and securing both edges of the chicken breast with 2-3 toothpicks or more until it holds together. Repeat with each chicken breast. 

Heat a large cast-iron skillet over medium/high heat. Add olive oil. When the olive oil is fragrant add the stuffed chicken breast to the pan. Sear for 2-3 minutes on each side to brown.

Carefully place the cast iron skillet in the oven (be careful, the handle might be hot) and bake at 375ºF for 30 minutes, flipping halfway. 

Use a meat thermometer to check the internal temperature of the chicken breast. Make sure it's at least 165ºF before removing it from the oven. Let rest for at least 5 minutes before eating.